1. Field of the Invention
The present invention relates to equalization circuits in general and in particular to a circuit that enables the equalization of loudspeakers to be automatically switched when an optional subwoofer is added to an entry level two-speaker audio system.
2. Description of Related Art
When a pair of loudspeakers are designed for listening to music or any other program material, the equalization to those speakers is normally optimized for full range frequency operation, commonly 20 Hz-20 kHz. Active and/or passive filters are required to obtain flat frequency response for full range operation and these types of filters are commonly used in loudspeaker systems to correct for non-uniform frequency response. Transducers which are small and inefficient are not optimum for low frequency operation; however, due to cost considerations and/or lack of available space inside smaller loudspeaker enclosures (such as multimedia speakers), these small transducers are commonly used despite their relatively poor ability to reproduce low frequencies and despite limited power handling capacity. A 2.5 to 3 inch diameter transducer, for example, may only be effective down to 200 to 300 Hz, whereas typical program material extends down to approximately 20 Hz. These smaller transducers are better suited as satellite speakers for handling mid to high frequency program material.
When a subwoofer is added to a loudspeaker system, the low frequency information in the program material will be handled by the subwoofer; however, if the smaller, less efficient transducers are still subjected to those same low frequencies and high excursion, they needlessly labor to reproduce low frequencies, consuming excess power, causing the speaker to distort and causing the sound quality to be less than optimum. The system is not smart enough to know that the subwoofer has been connected. Thus, in the prior art, if a subwoofer is desired to be added to the system, a manually operated switch or switches must be used to change filters that are connected to the left and right speakers and to route any signals to the subwoofer.